Research Paper on "UNIX vs. Windows Operating System Architectures Date"

Research Paper 6 pages (2430 words) Sources: 5

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UNIX vs. Windows Operating System Architectures

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Microsoft Windows and UNIX operating systems have achieved significant adoption in enterprises globally based on their proven reliability in demanding computing environments and ability to scale in support of complex transactions and network workflows (Maurno, 2005). The intent of this analysis is to evaluate the UNIX and Windows operating system architectures on the basis of differences in their kernel architectures, application programmer interfaces (API), security, approaches to process management. Both operating systems can support shell scripting, with this approach to process management and exception handling being more prevalent on the UNIX platform (Takeuchi, Nakayama, 2006).

Comparing Kernels and Application Programmer Interface (API)

The design of each operating systems' kernel is significantly different, varying on how each support I/O management, memory management, scheduling, power and thread management. One of the most significant differences between the kernels of these operating systems is how each define and use subsystems for completing application development while supporting deployment, delivering a high level of reliability at the system level (Janssens, Annot, van de Goor, 1986). The UNIX operating systems' architecture is divided into three levels, with the lowest or most fundamental level being the kernel, which is responsible for scheduling tasks, managing resources and controlling all aspects of operating system security (Hontanon, 1999). One of the most significant differences between the UNIX and Windows operating system architectures is that the former recompiles the system-level kernel at runtime. Database developers have favored the UNIX platform as a development environment as a result of this feature, as it makes the task of troubleshooting application development much more accurate and efficient (Son, Lee, Jeon, Chung, Lee, Lee, 2011).Conversely the kernel architecture of the Windows operating system does not re-compile and is not as customizable as the UNIX kernel.

Another variation in kernel architectural design that directly affects how customizable both operating systems are is the design philosophy with regard to monolithic vs. hybrid kernels (Zhou, Goscinski, 1997). The UNIX operating system kernel is considered monolithic in that it supports the main operating systems services including the main kernel thread that defines the use of memory. Developers prefer to code on platforms with monolithic kernels when there is intensive use of device drivers, system resources and the need for advanced memory management, in addition to file management (Zhou, Goscinski, 1997). A monolithic kernel contains all device-level intelligence as well, which is a point of reliability if a device driver fails to function, which would lead to an entire system crashing. The Windows operating system architecture is designed with a hybrid kernel architecture, allowing for greater customization and modularity, including the ability to significantly change application performance through application programmer interface (API) calls.

There are also basic foundational differences in how the Microsoft Windows and UNIX operating system architectures are designed, each following a completely different philosophy with regard to support for application development, security and long-term reliability (Maurno, 2005). While there are many variations of the UNIX architecture, they all share three levels of functionality in common which include having the kernel at the lowest level of the architecture. The kernel, which is monolithic in that it supports all resource and memory-based sharing tasks of the operating system, also manages all resources and all security tasks including the secure scaling of the operating system across multiprocessor environments (Janssens, Annot, van de Goor, 1986). This aspect of the UNIX kernel has continued to gain importance as enterprise looks to scale their databases and applications that rely on them across broad geographical and system-based resources (Son, Lee, Jeon, Chung, Lee, Lee, 2011). At the next level of the UNIX architecture is the shell or the user interface, which is used for interpreting user commands and starting applications. This is the level of the architecture where UNIX system administrators spend the majority of their time writing shell scripts for managing processes. In the Process Management section of this paper a sample shell script is provided as an example. At the third level of the UNIX operating system architecture, tools and command utility functions are supported. As the kernel is the foundation of the UNIX operating system, it must scale to support all of these functions and also track memory and resource usage over time. The monolith nature of UNIX kernels is illustrated in Figure 1, which is a generic representation of what a typical kernel looks like from a design and functionality standpoint.

Figure 1:

Basic UNIX System Kernel Example

Source: (Janssens, Annot, van de Goor, 1986)

In contrast to the monolithic nature of the UNIX kernel, the Microsoft Windows operating system kernel is more hybrid in design, comprised of a series of modules. Microsoft chose to create a more hybrid-based kernel architecture as this type of kernel has faster development times for drivers within the modules themselves, as no reboot is required if only a module of the operating system is being used. This is a lesson learned from UNIX kernel development that Microsoft chose to deliberately emulate at the module level. Microsoft has also designed their subsystems to have a greater variety of APIs to support specific function calls, which further streamlines this operating systems' integration into networked environments (Iyer, Lee, Venkatramen, Vesset, 2007).

The Microsoft hybrid kernel approach is also deliverable designed to allow for greater support of faster and more secured integration to 3rd party platforms through a wide variety of network protocols including TCP/IP. DHCP, XML and TELNET sessions as defined in UNIX shell scripts (Vellalacheruvu, Kumar, 2011). Figure 2 to the right shows the Windows 2003 Server architecture as an example.

Figure 2: Windows Server Architecture Source: (Vellalacheruvu, Kumar, 2011).

Unlike UNIX, the kernel mode is designed for rapid performance and ease of integration to 3rd party computing environments. Microsoft chose to have the Logon Process, Win32 application, Interix/POSIX subsystem, Win32 subsystem and Security Subsystem reside in the User Mode of their operating system architecture to make them more agile, and less constrained by kernel mode constraints. Microsoft began setting security as a strategic design priority during the 2001 and 2002 development cycles, and this approach to defining the Windows architecture allowed for complete revisions and updates to the Security Subsystem if necessary to keep the technology current against threats (Vellalacheruvu, Kumar, 2011).

In analyzing the differences between UNIX and Windows at the subsystem level, the inclusion by Microsoft of Windows subsystems for Win32, POSIX and Windows Services for UNIX are present in User Model to allow for greater customization to specific enterprise users' needs. Microsoft designed Windows Services for UNIX to support 300 different UNIX commands including KornShell, C Shell and the common commands of awk and text editor vi for example. The high degree of modularity of the Microsoft Server system architecture is easily customizable yet also presents security risks as well (Hartley, 2008). The section of this analysis dedicated to security analyzes those differences in the operating system architectures.

Analysis of API Differences

In UNIX, the API commands and syntax are often referred to as system calls. A system call is actually a procedural command into one of the modules of the monolithic kernel, and is often used for changing device parameters or enabling integration to third-party devices and functions. UNIX APIs vary significantly across releases and also have begun to proliferate Linux operating system distributions as well. APIs in UNIX are most effective when programmed at the kernel level to ensure the optimal performance of the application software and system modifications being made. As a result, APIs in UNIX often will impact overall system performance across all devices and can either drastically improve or degrade total application and server performance based on the quality of programming completed (Iyer, Lee, Venkatramen, Vesset, 2007). This becomes especially evident in database development and programming on the UNIX platform (Son, Lee, Jeon, Chung, Lee, Lee, 2011). The Microsoft API strategy is completely different and concentrates on creating emulations of different operating system kernels. In the Microsoft architecture, kernels are also located at the User Level which makes their APIs more efficient and customizable through customized development. As a result of this design philosophy, the Windows architecture supports subsystem APIs for its native Win16 and Win32-based applications, in addition to support for UNIX (POSIX) systems with a series of APIs that emulate UNIX commands.

Analysis of Security Differences at the Architectural Level

User authentication and security models vary significantly between UNIX and Windows operating system architectures. Both support single sing-on authentication yet the differences in how user authentication is managed over domains illustrates the differences in design philosophy of the two operating systems. In UNIX, a user can log into any system on a network they have a valid user and password for. The Network Information System (NIS) Domain acts as the validation point. In larger system installations and networks, the NIS may actually be a network of systems integrated together. User authentication data is often stored in a specific database with a taxonomy… READ MORE

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